1. Field of the Invention
This invention relates generally to a thin-film magnetic head used for recording and reproducing information in magnetic disk units, and more particularly to a thin film magnetic head comprising a lower magnetic core and an upper magnetic core disposed facing each other via a non-magnetic thin film serving as a magnetic gap, and thin film coils wound between the upper and lower magnetic cores, in which thin film conductors constituting the thin film coils have a cross-section of such a shape that an insulating resin is easy to fill in the space between the conductors.
2. Description of the Related Art
A separate recording/reproduction type magnetic head comprises a magneto-resistive head and an inductive head laminated on a non-magnetic substrate 101 made of a material, such as alumina/titanium carbide, as shown in the perspective view of FIG. 3. The separate recording/reproduction magnetic head which is manufactured with thin film technology is often called as "thin film magnetic head" as a whole. The inductive head has also heretofore been called the "thin film magnetic head," as against the magneto-resistive head. In this Specification, therefore, the term "thin film magnetic head" is used as referring to the "separate recording/reproduction type magnetic head" and/or the "inductive head."
In FIG. 3, a thin film magnetic head has on a non-magnetic substrate 101 an alumina layer 111, a lower shield 102, a magneto-resistive element 103, a magnetic film 105 serving as an upper shield and a lower magnetic core (hereinafter referred to as "lower magnetic core"), and an upper magnetic core 107. In the figure, an insulating film for insulating between the lower shield, the magneto-resistive element and the upper shield is omitted. As shown in FIG. 4 illustrating the longitudinal section of the head shown in FIG. 3 in the gap depth direction, the head has a non-magnetic thin film 115 comprising alumina, etc. between the lower magnetic core 105 and the upper magnetic core 107. The non-magnetic thin film 115 serves as a magnetic gap, through which opposing ends of both magnetic films form magnetic poles 105' and 107' of the thin film magnetic head.
An exciting coil 106, 106' is wound between the lower magnetic core 105 and the upper magnetic core 107. A thin film coil is used as the exciting coil, with the number of turns of this coil being normally 10 to 15 turns to maintain the magnetic and electric conversion characteristics between the upper and lower magnetic cores and the coil. In order to reduce the inductance of the head by reducing the space occupied by the coil between the upper and lower magnetic cores, it has been commonly practiced to dispose the thin film coil in multiple, normally two, layers. A non-magnetic insulating resin layer is provided between the thin film conductors of the coil to insulate between the thin film conductors, and between the thin film conductors and the magnetic cores. FIG. 4 is a cross-sectional view of the one having thin film coils arranged in two layers. As shown in the figure, an insulating resin layer 116 is formed on a non-magnetic thin film 115 deposited on a lower magnetic core 105. Since the non-magnetic thin film 115, made of alumina, etc., serves as a magnetic gap for the thin film magnetic head between both magnetic cores, the thickness thereof is as thin as 0.3 to 0.4 .mu.m, about the length of the magnetic gap. The insulating resin layer 116, however, is required to have a certain thickness, about 1.5 to 2.5 .mu.m, for example, because the shoulder of the magnetic pole 107' at the end of the upper magnetic core 107 rests on part of the insulating resin layer 43, defining the apex of the magnetic head.
Thin film conductors of the bottom-layer thin film coil 106 are arranged in parallel with each other on the insulating resin layer 116. Another insulating resin layer 117 is provided in such a manner as to enclose the lowermost-layer thin film coil 106. Thin film conductors of the upper-layer thin film coil 106' are formed in parallel with each other on the insulating resin layer 117, and still another insulating resin layer 118 is provided in such a manner as to enclose the upper-layer thin film coil 106'. On the insulating resin layer 118 formed is an upper magnetic core 107. A magnetic path for the thin film magnetic head is formed through the upper and lower magnetic cores 107 and 105. And, numeral 119 presents a filler material, such as alumina.
In the following, the manufacturing method will be described. Thin film coils for the thin film magnetic heads are manufactured by copper plating. A conductive film is deposited by sputtering a conductive material, such as copper, on a non-magnetic thin film 115, made of alumina, and an insulating resin layer 116 laminated on the lower magnetic core. Next, a photoresist film is applied to the surface of the conductive film and baked at a predetermined temperature. A photomask is positioned and aligned on the photoresist film, which is exposed, developed and rinsed with water. With this, a photoresist pattern matching the shape of the thin film coil is formed. Next, coil conductors are deposited by plating using a plating solution, such as copper sulfate. After the photoresist film has been stripped, the conductive film between the coil conductors is removed by ion milling to complete a helical coil 106. Photoresist is poured on this coil in such a manner as to enclose the coil, and heated for cure at about 270.degree. C. to form an insulating resin layer. In order to form a multi-layer coil, this process is repeated.
With the ongoing trend toward higher recording density in the field of magnetic recording, the size of thin film magnetic heads is being increasingly miniaturized. The portions that can be miniaturized include intervals between coil layers, between the upper magnetic core and the coil, or between adjoining coil conductors (usually referred to as coil pitches). Reducing coil pitches, however, would make it difficult to fill the spaces between coil conductors with insulating resin. In particular, when the height of the thin film conductors is larger than the width thereof, or when the cross-sectional shape of the thin film resin is of an inverted trapezoidal shape, it could be difficult to completely fill the spaces between the thin film conductors with insulating resin, often causing cavities. Subjecting thin film magnetic heads with cavities to heat treatment and other subsequent processes could result in shrinkage of insulating resin in the vicinity of the cavities, leading to distortions of conductors and magnetic cores. FIG. 4 is a cross-sectional view of a thin film magnetic head of such a type, in which a cavity 120 tends to be caused on the conductor side surface. Even with the upper surface of the conductors being convexedly curved, if the inclination of the conductor side surfaces is larger than 90.degree., the conductive film near the conductor side surfaces tends to be left unremoved when the conductive film is removed by ion milling. This is attributable to the fact that part of the upper surface of the conductor acts as an umbrella, preventing ion particles from impinging on an area near the conductor side surface. The presence of part of the conductive film left unremoved near the side surface could readily cause an electrical short-circuiting in the adjoining conductors. A current leak in these areas could cause the resistance and inductance of the coils to change, resulting in changes in the size of recording magnetic field to be produced on magnetic poles.
To reduce the spaces between the coils and the upper magnetic core, it is a common practice to reduce the thickness of the insulating resin layer deposited on the coil layer. In doing so, however, the thickness of the insulating resin layer tends to become thinner on the upper edges of the thin film conductors of the coils, causing a short-circuiting between the upper magnetic core and the thin film conductors. The term upper edges of the thin film conductors used here refers to corner portions on the upper surface of the thin film conductors, or portions near the boundary between the upper surface and the side surface. When a photoresist of a low viscosity is used to completely fill the space between the thin film conductors, the photoresist formed tends to become thinner at the upper edges of the thin film conductors. Using a photoresist of a higher viscosity to a sufficiently thick insulating resin layer to cover the upper surface of the thin film conductors, on the other hand, could lead to an incomplete penetration of the photoresist into the space bottom between the thin film conductors, causing cavities. These defects, if produced, could lower yields in the manufacture of thin film magnetic heads.